This invention relates to gauges and particularly to a gauge for measuring the rate of ascent for scuba divers.
The rate of ascent is critical to the prevention of serious, even potentially fatal, lung and brain damage. Boyle's Law states that if the temperature is kept constant the volume of a gas will vary inversely with the absolute pressure while the density varies directly. This means that if the pressure on a gas is doubled, the density too is doubled but the volume is decreased to one-half the original volume. In seawater each 33 feet (34 feet for fresh water) in depth is equal to one additional atmosphere of pressure (14.7 psi). For this reason, when divers have completely filled their lungs with air at a depth of 33 feet, their lungs are holding twice as much air as when filled at surface level. For each 33 feet additional in depth, the volume of air needed to fill the lungs is increased accordingly. At 66 feet, the water exerts additional pressure of 29.4 psi (two atmospheres of pressure), so that the total pressure is 44.1 psi or three atmospheres of pressure, and a diver's lungs will hold three times as much air as when filled at surface. The density is, therefore, actually three times greater than it was at the surface, but the volume is one-third less.
The most serious damage the lungs can suffer in diving is from the expansion of air as a result of pressure reduction. If air is taken into the lungs and held in at a depth of 125 feet, it will increase five times in volume if a diver moves quickly to the surface where the external pressure is proportionately reduced to one-fifth. It is easy to understand how lung damage could be serious, even fatal, is a diver held his breath while surfacing.
If a diver fills his lungs with air while at depth to the size they are normally on the surface, and then ascends, the lungs will progressively expand. If the lungs are not emptied of air fast enough during the ascent, rupture of membranes and capillaries may result, permitting air to enter the bloodstream. This would be an air embolism. Air embolisms are caused by air being forced through the lung walls into the bloodstream, when holding one's breath, while ascending with a breathing apparatus. They can occur when one ascends from a depth as shallow as 7 feet. At the outside pressure decreases, the inside pressure of your lungs simultaneously increases, and when you reach the surface of the water, such overexpansion (like that of a toy balloon) reaches the breaking point with a possible rupture of the lung and subsequent leakage of air bubbles from the lungs into the bloodstream. Air bubbles are apt to lodge in the brain and cause permanent damage or death.
Other dangers of ascending too rapidly include spontaneous pneumothorax and subcutaneous and mediastinal emphysema. Spontaneous pneumothorox is caused by air getting into the space between the lungs and the lining of the chest wall causing the lung to collapse, particularly at least, as pressure increases. Enough such pressure will seriously impair breathing and heart action. Subcutaneous and mediastinal emphysema is caused by the expansion of air upon ascent in the tissue spaces of the mediastinum (air space in the middle of the chest). Whatever the degree of emphysema, air embolism and its associated dangers may be present.
It has been found that in making a free ascent a diver's rate of ascent should not exceed 60 feet per minute. During ascention the air volume in the diver's lungs will increase with the lessening of water pressure. The diver must exhale continually as he rises. If the diver senses a slight pressure pain in the chest, he is beginning to feel the effects of overexpansion, meaning that he is either rising too fast or not exhaling adequately. However, an air embolism can occur without warning of pain. The crucial point of ascent occurs in the last ten feet, where pressure change is the greatest. From this depth upward, the diver must exhale as vigorously as possible.
As stated above, the rate of ascent is critical to the prevention of serious, even potentially fatal, lung and brain injury. Studies have been done which show that a large percentage of all divers ascend too rapidly thereby risking air embolism. The proper rate of ascent is 60 feet per minute or less.
At this time the most common method taught for controlling the rate of ascent is for the ascending diver to watch his air exhaust bubbles and to rise no faster than the bubbles. This method is not reliable for several reasons. Bubbles speed up as they reach the surface which may cause too rapid an ascent during the depths of greatest pressure change. Bubbles are not that easily visible and are especially difficult to track in murky water when also watching out for other divers and boats.
A diver could also use, in combination, a dive watch and a depth gauge. From this the diver could calculate his rate of ascent. However, this is not always practical and is difficult to accomplish with accuracy. Depth gauges are not graded fine enough to show ascent levels accurately. Because of the need to watch two separate devices at the same time, safe ascent procedures cannot be followed. The basic safe procedure is for the diver to hold a hand over his head while slowly circling looking for boats or other obstacles.
The two above methods are difficult for the diver. There are no reference points. The physics of the expanding air on buoyancy increases the ascent speed. And finally, the ascending diver must keep a close watch for boats when surfacing.
The prior art includes various devices which attempt to aid the diver in depth measurements and rates of changes in depth. A number of depth gauges for divers have been patented. Included among these are: U.S. Pat. No. 2,935,873, "Diver Held Depth Gauge"; U.S. Pat. No. 2,986,038, "Wrist Pressure Gauge"; U.S. Pat. No. 3,831,449, "Depth Gauge"; U.S. Pat. No. 3,990,306, "Temperature Compensated Depth Gauge For Scuba Diving"; and U.S. Pat. No. 4,107,996, "Pressure Gauge". These are all sealed gauges for measuring depth. None have the ability in themselves to measure rate of change in depth against critical ascent speed.
The prior art also includes a device called Dive Bubbles. The device is an ascent control device and follows the bubble theory described above. In theory, a small ball is released from a special holder and rises through the water at the ascent rate required by dive tables. Since the Dive Bubble is based on the bubble theory, it does not solve the problems associated with the air exhaust bubbles. The diver must watch the ball as it rises. This precludes the diver from turning around and watching for boats and other obstacles. The ball increases speed as it gets closer to the surface. If the diver stops or slows down, he is required to release another ball. There is no gradiation ability. After each dive, the diver must chase and recover the floating balls or replace them at additional cost.
Another device on the market designed to assist divers during ascents is the Deco-Brain. This is a solid-state electronic dive computer which consolidates the functions of the watch, depth gauge, diving table and decompression meter. A red warning light blinks if the diver's ascent rate exceeds 33 feet per minute. If the red light blinks in one second intervals or less, the ascent is between 33 feet and 39 feet per minute. If the red light is continuously illuminated, the ascent rate is approximately 66 feet per minute. There are no other gradations. The unit requires batteries and there are conditions under which the diver cannot determine if the device is working. The device is bulky and expensive.
The present invention comprises a relatively inexpensive mechanical gauge for for warning a scuba diver of an unsafe rate of ascent. The gauge is worn on the diver's wrist to monitor ascent speed. As the driver rises, water is passed through the gauge against a float causing an indicator to move. If the diver ascends too quickly, the indicator will move into an unsafe zone thereby signaling to the diver that he is rising too fast.
Accordingly, an object of this invention is to provide a new and improved gauge for warning scuba divers of an unsafe rate of ascent in the ocean or sea.
Another object of this invention is to provide an ascent gauge which is inexpensive and easy to use while allowing the diver to follow safe ascent procedures even under adverse conditions.
A more specific object of this invention is to provide a new and improved ascent gauge for scuba divers which includes a float indicator calibrated and designed to react against the flow of water into the gauge thereby indicating to the ascending diver his safe and/or unsafe rate of ascent.